When it comes to the serious business of child's play, most parents simply don't have what it takes. My nine-year-old recently gave me incontrovertible proof that I was one of these failures in the fun department. She had spent the night at the house of one of her friends. She likes going there, she told me, because after supper, "The mum and dad play board games with us (pause for maximum effect) for a very long time. And even when it's not a Saturday."

The idea of doing anything very much after supper apart from sitting comatose on the sofa, holding, if not reading, a newspaper, is sufficient to trigger in me a sense of extreme fatigue. The thought of a three-hour marathon game of Monopoly, or acting out the bit in Harry Potter and the Prisoner of Azkaban, when Hermione throws a punch at Malfoy, again and again, is likely to produce a bout of nervous exhaustion. But nothing can assuage my guilt.

Today is Playday, the UK's largest annual celebration of play, now in its 17th year. More than 100,000 children will attend dozens of events, including the conversion of Trafalgar Square into a playground. The occasion has been coordinated by the Children's Society in partnership with the Children's Play Council. Playday promotes an admirable cause - children's right and need to play - while also campaigning to provide opportunities for them to do so.

Research tells us that the kind of play that allows an element of risk and exploration and challenge, supported - but not policed by - grown-ups, is as vital to a child's development and quality of life as literacy and numeracy. Earlier this year, the government published Getting Serious about Play: a Review of Child's Play, designed to establish the principles by which £200m of lottery cash from the New Opportunities Fund will be spent, focusing particularly on provision for the disabled and the marginalised living in deprived areas.

Frank Dobson, who chaired the six-month review, defined the concept of play as, "What children do when they are given the freedom to follow their own ideas and interests in their own way and for their own reasons."

Through play, says Tim Gill, director of the Children's Play Council, the young acquire confidence and independence. "They learn not just physical skills but how to socialise, how to solve problems and how to handle success and failure."

All of which assumes that play is a group activity as well as a solitary exercise - and that it does not involve several hours in front of the television set, failing to burn up the calories, consumed as the afternoon wears on.

Studies tell us that the vast majority of parents understand the importance of the theory of "free" play - although that still doesn't stop some of them from turning it into a highly-organised and subscribed branch of education. Or, they insist that everyone does exactly what they say - or they are going to tell.

Another difficulty is that we live in a time-squeezed adult society in which every minute counts and control is deemed vital. Paid work also often steals the time a parent might otherwise spend with a child. All these pressures are completely contrary to the essence of successful play - that it is unending, fluid, anarchic. In my own case, I admit to being a bit of a clock-watcher. I'm not bad at building tents in the bedroom; dressing Bratz dolls and sticking bits of cardboard together. However, I am occasionally reprimanded for being present in the flesh but absent in mind and spirit. "Why do you look as if you're somewhere else?" both daughters have been known to complain from time to time. Probably, because I am.

The government is considering offering parenting classes not just to those adults whose offspring are considered vulnerable but to anyone who is willing to attend. Classes are likely to include suggestions not just on what to play at different stages of a child's life, but also how to play (back off: you're the adult). Since people appear far more willing these days to own up to not having much of a clue about aspects of parenting (without risk of an invasion of social workers), this could be good news for children.

Lisa Knapett is a single mother of five children, aged three to 14; she co-chairs the East Peckham Sure Start Parents Forum, and has just qualified as a volunteer to teach other parents how to play. She says it is difficult to find games that all her children want to play together - or to find sufficient time for them individually, so they each have after-school activities, such as Brownies, and she arranges a lot of day trips in the holidays.

"We live in a three-bedroom flat, and the younger ones get all the toys out, but we have big clearing up sessions at the end of each day. In the holidays, I try to arrange for us to be out as much as possible.

"Playing with the children has got easier now. When I was a young mother with two children, I didn't have a family network around me so I joined mother and toddler groups and learned as I went along. Play is about being open-minded and not trying to take over. I let them lead me and do what they want. My mum never played with me and I always remember playing on my own. So, I took a real pleasure in playing with my children. I'm creative so we do colouring and writing and lots of arts and crafts. I really enjoy sitting down in the evening, cuddling up and reading a story. I'm quite busy but I believe it's quality not quantity time that counts."

A recent poll commissioned by the Children's Society gauged how often parents and children play together. While most parents (72%) said they played with their children daily - the majority of the young, aged from seven to 12, said their parents played with them either rarely or never. Whatever grown-ups think they are doing, it is not being classed as a bundle of fun.

Children reported that adults failed to play because they were either too busy or too tired; or the children themselves opted not to play because a parent was too bossy; or didn't know how to play the games - or because friends were better company. One seven-year-old said, "I think it's sometimes a bit harder for older people to play because they lose their imagination."

Craig Dwyer is father of two children, Thomas, six, and Imogen, four. He works long hours at the BBC and sometimes has to travel. His wife, Anne, is a full-time mother. "If I can arrange it, I'm home at around 7pm for bedtime and books," he says. "The weekend is the time for more adventure, riding a bike or football. The difficulty is that Thomas and Imogen often want to go off in different directions out of spite as much as anything else. Both are very creative and love to make things. I'm not as free; I'm always clearing up.

"Sometimes I find it difficult to switch after a hectic day to a mood for play. It's as if I haven't had time to decompress and as soon as you open the door, the children are full on.

"My wife is very playful with the children, she's always keen for them to exercise their freedom and she encourages them to explore. My parents didn't play with me that much but then I lived in Kent and it was easier for us to roam around. In London, it's much more difficult for children to discover independence."

The Children's Society and the Children's Play Council are urging parents to be more "playful" and, today, to take half a day for play. Tim Gill says, "Playful parenting is about putting to one side our adult cares, engaging with our children and having fun."

The trouble is that it all sounds a bit coy and forced - like asking a great aunt to tango under the delusion that it will bring zest back into all aspects of her life. Play has to be brought much more to the foreground of the public arena (not least as a counterweight to the view that children are always a problem). But that also requires more family-friendly flexibility in the work place. It is also handicapped by the government's apparent determination to turn each child's every waking minute into preparation for the next stage of schooling. Skipping? Goodness me no - not unless you count the skips and divide by five!

In the 60s, fun was a central part of the hippy philosophy. Somehow, ever since, adults have grown progressively more serious: too grown-up for their own good. So, how do we, as adults, learn to switch off, cool down, and tune in to a world that is only a child's imagination away? Perhaps we could start by asking the experts - our sons and daughters. And take the time to listen.

· Events for Playday and The Children's Society's "Ten tips for playful parenting" can be found at www.playday.org.uk.